706 PllOCKKDIXGS OF THE NATIONAL MUSE I'M. v,.i.. xxn. 



slope radially plicate ; epidermis dark ; pseudocardinals stumpy, radial, 

 graii ularly striate; laterals double in the left valve, single in the right, 

 with a faint, secondary ridge below; anterior muscle scars deep, nearly 

 smooth ; cavity of the beaks moderate, slightly compressed. 

 Animal unknown. 



tUNIO SLOATIANUS Lea. 



*l'nio sloatianus LEA, Pr. Am. Phil. Soc., I, 1840, p. 287; Tr. Am. Phil. Sex., 

 VIII, 1842, p. 217, pi. xvi, fig. 33; Obs.,111, 1842, p. 55, pi. xvi, fig. 33. 



* H. and A. ADAMS, Gen. Eec. Moll., II, 1857, p. 497.* CHENU, 111. Conch. 1858, 

 pi. xxxn, figs. 7, 7a, 76.* KUSTER, Conch. Cab., 1862, p. 286, pi. xcvi, fig. 3. 

 ' B. H. WRIGHT, Check List, 1888. * P^TEL, Conch. Sam., Ill, 1890, p. 167. 



* Marr/aron ( Unio) nloatianus LEA, Syu., 1852, p. 21 ; 1870, p. 31. 



" Fleet o met- it s sloatianus CONRAD, Pr. Ac. N. Sci. Phila., VI, 1853, p. 261. 



* Unio atromarginatus LEA,' Pr. Am. Phil. Soc., I, 1840, p. 288; Tr. Am. Phil. Soc., 



VIII, 1842, p. 207, pi. xiii, fig. 21; Obs., Ill, 1842, p. 45, pi. xm, fig. 21. 



* H. and A. ADAMS, Gen. Rec. Moll., II, 1857, p. 488.* CHENU, 111. Conch., 1858, 

 pi. xxvin, figs. 6, 6a, Qb. * KUSTER, Couch. Cab. Unio, 1861, p. 250, pi. 

 LXXXIV, tig. 2. * B. H. WRIGHT, Check List, 1888. *P^ETEL, Conch. Sam., 

 Ill, 1890, p. 145. 



* Maryaron ( I'nio) atromarginatus LEA, Syu., 1852, p. 19 ; 1870, p. 29. 



* Plectomerus atromarginatus CONRAD, Pr. Ac. N. Sci. Phila., VI, 1853, p. 260. 



* Unio aratus CONRAD, Ann. and Mag., IV, 1849, p. 302; *Pr. Ac. N. Sci. Phila. IV, 



1849, p. 154. 



* Unio plectophorus CONHAD, .11. Ac. N. Sci. Phila., 1, 1850, p. 277, pi. xxxvni, fig. 7. 



* Plectomerus plectophorus CONRAD, Pr. Ac. N. Sci. Phila., VI, 1853, p. 2. 



Chattahoochee and Flint rivers, Georgia. 



(Group of Unio crassidens.) 



Shell generally solid, rather inflated, rhomboid oval, with a sharp, 

 well-developed posterior ridge; beaks prominent, the sculpture consist- 

 ing of a few coarse ridges running nearly parallel with the growth 

 lines and swollen at the posterior ridge; surface of the valves nearly 

 smooth or only marked by growth lines; posterior slope bearing 

 wrinkled, corrugate, radiate ridges; epidermis often faintly rayed. 



Animal having the branchiae very large, rounded below, inner the 

 larger, free nearly or quite their entire length from the abdominal sac; 

 branchial and anal openings large, with many small papillae ; marsupiuui 

 occupying the entire outer gills. 



tUNIO CRASSIDENS Lamarck. 



*Unio crassidens LAMARCK, An. sans Vert., VI, 1819, p. 71. * LEA, Obs., I, 1834, 

 p. 199. *DESHAYES, An. sans Vert., 2d ed., VI, 1835, p. 532; 3d ed., II, 1839, 

 p. 667. *HANLEY, Test. Moll., 1842, p. 184; ' Biv. Shells, 1843, p. 184, pi. xx, 

 fig. 46.* CATLOW and REEVE, Conch. Norn., 1845, p. 58. *H. and A. ADAMS, 



'Lea's type of sloatianus is an old, arcuate shell, while the type of atromarginalus 

 is young and quite different looking. But the young plicate (tiromarginatus gradually 

 changes into the smoother sloalianus as it grows older, :md specimens of both show 

 the dark bordered nacre, though it is more pronounced in the young shells. 



